/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.iotdb.library.drepair.util;

import org.apache.iotdb.udf.api.access.RowIterator;
import org.apache.iotdb.udf.api.exception.UDFException;

public class ARFill extends ValueFill {
    // TODO Higer order AR regression
    private int order = 1;
    private double theta = 1e10;

    public ARFill(RowIterator dataIterator) throws Exception {
        super(dataIterator);
        calMeanAndVar();
    }

    public void setOrder(int order) {
        this.order = order;
    }

    @Override
    public void fill() throws UDFException {
        // compute \sum x_t * x_{t-1}
        double acf = 0;
        double factor = 0;
        int acf_cnt = 0;
        for (int i = 0; i < original.length - 1; i++) {
            double left = original[i], right = original[i + 1];
            if (Double.isNaN(left)) {
                left = 0;
            }
            if (Double.isNaN(right)) {
                right = 0;
            }
            acf += left * right;
            factor += left * left;
            acf_cnt += 1;
        }
        if (factor == 0d || this.theta >= 1) {
            this.time = new long[]{0};
            this.repaired = new double[]{0D};
            throw new UDFException("Cannot fit AR(1) model. Please try another method.");
        }
        // acf /= acf_cnt;
        this.theta = acf / factor;
        double mean_epsilon = 0;
        double var_epsilon = 0;
        double cnt_epsilon = 0;
        for (int i = 0; i < original.length - 1; i++) {
            double left = original[i], right = original[i + 1];
            if (Double.isNaN(left) || Double.isNaN(right)) {
                continue;
            }
            cnt_epsilon += 1;
            double epsilon = right - left * this.theta;
            mean_epsilon += epsilon;
            var_epsilon += epsilon * epsilon;
        }
        if (cnt_epsilon == 0d) {
            this.time = new long[]{0};
            this.repaired = new double[]{0D};
            throw new UDFException("Cannot fit AR(1) model. Please try another method.");
        }
        mean_epsilon /= cnt_epsilon;
        var_epsilon /= cnt_epsilon;
        for (int i = 0; i < original.length; i++) {
            double yt = original[i];
            if (!Double.isNaN(yt)) {
                repaired[i] = yt;
            } else {
                if (i != 0) {
                    repaired[i] = this.theta * repaired[i - 1] + mean_epsilon;
                } else {
                    repaired[i] = this.mean;
                }
            }
        }
    }
}
